Purification of naphthalene



Patented Apr. 2, 1935 1 t l i UNITED STATES A'iENT OFFICE PURIFICATION OF NAPHTHALENE James Todd and Jay .0. Owens; Chicago, 111., assignors toThe Sherwin-Williams Company, Cleveland, Ohio, a corporation'of Ohio No Drawing. Application December 1'7, 1931,

' SeriaLNo. 581,773

'- 8 Claims. (o1. zen- 168) The present invention relates to the purifica- In practicing the invention it is not necessary, tion of naphthalene particularly by distillation nor perhaps desirableyto dispense entirely with methods. v g I acid washing. Thismay be done, as it'has been Naphthalene may be distilled by o'rdinaryapdone heretofore, toremove such substances as plication of heat to boil or vaporiz'e'thenaph may be conveniently. altered by acid and easily ,5

' tha1ene,and'a1so by introduction of'ga's orvapor; removed from the naphthalene by washing, as as bysteam distillation. Heretofore, crude naphwith water. Crude or-impure naphthalene may thaleneshaszbeensoidistilled at a' pI-I of? or over, also contain volatile substances, such asphenols or from a neutral oralkaline condition, or in and cresols, which are not rendered non-volatile other Words, in a non-acid'state. The distilled by acids. These substances are soluble in alka- 1o] product has'been then subjected to. acid washes, line solutions, and hence are easily removed by then to reagents for. neutralizing the acid,-and anialkali wash. Accordingly, the-naphthalene thenfagain vtodistillation. employed for thisinvention may. be or mayrnot The present invention aimsv to simplify the be washed with alkali, such .ascaustic soda bepurification of naphthalene by.distilling itfrom fore the acid distillation.

an acid condition. The distillation may be effected. in the pres-: A particular object of the invention'is simplience of strong or weak acids,.such as sulphuric fication'of the present methods. for purification or phosphoric acid, or various acidsalts which of crude'naphthalene. are acid in fact. The specific character of the" Another object of the invention is the use of acid radical appears not to be important, so long 29 an acidifying agent in a naphthaleneb'eing disas it is stable, or otherwise forms a reaction tilled; s 1 product which'is acid in character. This require- Still another object or the invention/is the ment excludes weakly acid oxidizing substances distillation of." naphthalene in the presence of such as potassium. dichromate. However, it is 25., an acid dissolved'therein. preferred thatit should notbe one which is dis- 5 Various; other and ancillary objects and ad'- tillablje in the presence of naphthalene under the vantages of the inventionwill become apparent conditions of distillation, such as hydrochloric from'th e following description and explanation acid. ,The latter is not excluded from the in-. of' theiinvention, which areggiven in connection vention for the reasonpthat it is not a preferred 30. with several detailed examplesof" the invention, 1 acid. It maybe used, and'although a part of it 30' as: it maybe used commercially; may be distilled over into the distillate, it does It is not necessary in explaining thisinvention V nevertheless function to cause other materials to refer specifically to the nature of impurities tov remain as a still residue. The acid which may foundincrude, or partially refined naphthalene. distill over mayberemoved' by a waterwash, These: may varyin character. and amount, acor may be entirely unobjectionable in-so-me uses 35 cording to theprevious history of the naphthaof the distillate. Where steam distillation is used lone-or thematerial from which the naphthalene for such a volatile acidthe condensate will comisderived. However, it appears that in the disprise an acid water which easily permits removal tillation of crude naphthalene; there passes over of the excess acid. 'Other volatile acids maybe 4,0 with the naphthalene, substance which is efused, such as acetic acid. A permanent hydro- 4Q fectively' removed by an acid wash or converted gen ion concentration below pH", as produced intoa non-distillable, or a less easily distillable by suitable acidsor acid salts, is the essential substance by acid, when acidis employed and C u of the success'ofany Suchacidic material. then neutralized. Ammonia base materials, such Sp cific acidsor acid salts are preferred b as. pyridin, are among the numerous impurities Cause Of th Certain advantages Obtained, 45 commonly. found. These in" particular are Theinvention may be carried out in numerous pable ofbombining'with acid to form complexes Ways for refining crude nap for whichfdoznot so readily volatilize. The present creasing the purity of any. imp r p e invention' is based. uponthe discovery that dis- It is 301731? necessary in each instance) pe tillation in the presence of acid:materially imm allthesteps disclosed inthe eXam p-les'herm 5 0 proves the distillate over that which isobtained inafter given as will appear from the Scope of from. aneutral or: from alkaline naphthalene, e invention as expressed in appended. and that'ifacid isused before distillation and/or e 1 during distillation,..itl is not'necessary to wash Examplel 5 with acidafterzdistillation. Commercialcrude naphthalene, usually melt- 5 ing from 76 C. to 78 C., may be heated above its melting point and preferably below the boiling point of water which may be later contained therein. For example, a temperature of 85 to 90 C. for the melted naphthalene is satisfactory. To 100 parts by weight of such naphthalene 3 parts by weight of concentrated sulphuric acid may be added, such for example as from 93% to 98% acid. It is to be understood that under these conditions such a strong acid may in part react with naphthalene, and produce one or more sulphonic acids and water. However, this is not an obstacle because (1) sulphonation cannot proceed too far, forming, water which stops the reactions, and (2) the sulphonic acids themselves are strong acids, and each is suitable per se as an acid for this invention. A mono sulphonic acid of naphthalene has been employed alone as an effective acid substance during distillation, using very little water in the mass.

. When the acid is added to the naphthalene the mixture may be agitated, and the agitation may be continued for, a short. time, such as 15 minutes. A longer time is not necessary but is not harmful. The time should be judged in accordance with the character of agitation, in order to assure complete contact of all the naphthalene with the acid. Then the mixture is allowed to settle forming two layers. The lower layer of acid or sludge may be drained ofi carrying with it a considerable quantity of the impurities. Some acid may remain as a residuum in solution in the naphthalene, or even in mechanical suspension. A small quantity, for example 1 part of very hot or boiling water may be added to wash the mass, agitation being used if desired. The layer of wash water is then drained oil. This merely aids in further removal of impurities and of the acid or the sludge layer. Thereafter water and more acid material is added for imparting to the mass an acid character for steam distillation. For example, 10 parts of water and 10 parts by weight of the same concentrated sulphuric acid may be added. Distillation may be efiected in any usual way, for example, and-preferably,

' by injection of live steam, supplemented by heat transfer from a steam coil. The distillate may 7 be drained from water of condensation leaving a refined naphthalene-" The dried naphthalene may have amelting point of '79.9 C.

Where much water is present in the naphthalene steam distillation is preferred. Where steam distillation is used, however, it is immaterial whether water is present in the naphthalene.

Nevertheless, where direct distillation is practiced, it is desirable that the amount of water in the naphthalene be minimized.

Example II I The naphtalene, substantially free from the added water, but'not necessarily entirely free, is distilled in the presence of 5 parts of sodium or potassium acid sulphate to 100 parts of original naphthalene base, using direct heat at atmospheric pressure.

The absence of large amounts of water, and the use of acid salt, is effective to keep bothwater and entrained acid, out of the distillate.

Example III The process of Example II may be repeated using in the distillation step the same propor-' tion of phosphoric acid as a substitute for the sulphuric acid salt. Vacuum distillation also may be practiced.

Example IV Heat 100 parts of naphthalene to to 0. While agitating, add 3 parts of sulphuric acid (93% to 98%). Continue agitation for 15 minutes. Allow to settle, and drain off acid sludge. Repeat the acid washing with a second addition of 3 parts of said sulphuric acid. Again drain 01f the sludge. Distill the residual naphthalene using direct heat at atmospheric pressure.

Sufficient acid here remains in the naphthalene to impart acidity to the batch during distillation. Sulphonic acids readily dissolve in napthalene and so dissolved function in the whole mass as the same is operated upon in this example.

Of the various mineral acids employed, it has been found that sulphuric acid is the best. This is no doubt due to the ease with which it forms sulphonic acids. A sulphonic acid of naphthalene is an example of an acid substance which is soluble in the naphthalene. Such an acid so dissolved more readily performs its acid functions on the impurities because of the better contact between acid and impurities, both being solutes in the naphthalene.

From the foregoing examples it will be readily apparent to those skilled in the art that numerous changes in operative manipulation and in materials may be employed without departing from the spirit and scope of the invention as expressed in the appended claims.

We claim:

1. The process of refining naphthalene which comprises distilling naphthalene from a mixture of impure naphthalene and an acid sulphate salt.

2. The process of refining naphthalene which comprises washing impure melted naphthalene with acid, removing excess acid leaving an acidifying residuum, adding water, and distilling naphthalene from the acidified washed naphthalene, the acid concentration at distilling temperature being insuificient to act chemically on the naphthalene.

3. The process of refining naphthalene which comprises washing melted impure naphthalene with a small quantity of concentrated sulphuric acid, removing the separable layer containing said acid, washing the residual melted naphthalene with water, removing the separable layer containing the water, adding to the residual naphtha lene an acidic substance, and distilling naphthalene from the acidified mixture, the acid during distillation being incapable of chemically acting upon naphthalene.

4. The method of purifying naphthalene which comprises adding not over about 5% of an acid substance to naphthalene and distilling naphthalene from the acid mass, said acid substance being capable under the conditions employed of remaining at least in substantial part unchanged by chemical union with naphthalene both preceding and during the distillation.

5. The method of purifying a batch of impure naphthalene which comprises adding to the naphthalene a small quantity of an acid substance and water sufficient to form an acid condition in the batch and distilling substantially all of said naphthalene from the acidified batch, the concentration and quantity of acid therein at the temperature of distillation being such as to prevent loss of any substantial amount of naphthalene by chemical union of acid and naphthalene, and the quantity further being such as to render the still mass permanently acid during the distillation. I

6. The method of purifying a batch of impure naphthalene which comprises adding to the naphthalene a small quantity of an acid substanceand water sufficient to form an acid condition in the batch and steam distilling substanbatch, the concentration and quantity of acid naphthalene a small quantity of an acid substance containing the sulphate ion and. water sufficient. to form an acid condition in-the batch, and distilling'substantially all of said naphthalene from the acidified batch, the concentration and quantity of acid therein at the temperature 1 of I distillation being such as to prevent loss of any substantial amount of naphthalene by chemical union of acid and naphthalene, and the quantity further being such as to render the still mass permanently acid during the distillation.

8. The process of refining naphthalene, which comprises washingimpure naphthalene with an aqueous alkali solution to remove alkali soluble impurities, washing the naphthalene thus treated with a concentrated acid to remove acid soluble impuritiesand washing with water to remove water soluble impurities, and distilling the naphthalene so treated in the presence of a small quantity of acid under conditions whichavoid any 20 substantial reaction with naphthalene and yet maintaining acidity throughout the distillation. JAMES D. TODD.

JAY C. OWENS. 

